The present invention generally relates to dielectric fluids used in capacitors and, in particular, to such fluids which include dioctyl phthalate.
Capacitor manufacturers usually produce many kinds of capacitors from different solid dielectrics For many years, polychlorinated biphenyls (PCB's) were used as an impregnant in the majority of capacitors due to its high dielectric constant, low dissipation factor, stability and no fire point. However, since PCB was banned by the U.S. government due to environmental, ecological and health hazards, many newly developed types of dielectric fluids are used in capacitors. For example, recently semi-aromatic/aliphatic esters (predominantly aliphatic) such as diisononyl phthalate (DINP), dioctyl phthalate (DOP) and others gained popularity as replacements for PCB.
Desirable properties for this fluid are: biodegradability, high dielectric constant, ease of refining, stability, high flash point, good gas absorber, and the ability to swell polypropylene film.
The present invention is directed to the provision of a dielectric fluid of an aliphatic ester that is a good gas absorber. A good gas absorber is needed in capacitor impregnants to prevent the cumulative effect of partial discharges producing a gas, and eventually leading to capacitor failure. The relative gassing rates of the capacitor impregnant should have a bearing on the corona start voltage, the corona extinguish voltage, and on capacitor life. Most gas being generated is likely to be a high "hot spot" area and improved gas absorption of impregnant is very desirable.
The dielectric fluid of the present invention also improves the swellability of polypropylene film capacitors. The advantages of swelling polymeric film is to reduce the space between the dielectric (film) and electrode and therefore increasing the intrinsic dielectric strength of the fluid. The swelling also restricts the movement of impurities resulting in low heat dissipation.